1. Field of the Invention
The present invention is concerned with a new method for measuring penile rigidity and with a new device for carrying out this method.
2. Brief Description of the Prior Art
Measurement of nocturnal penile tumescence hereinafter referred to as NPT, as developed by Fisher et al (see "The assessment of nocturnal REM erection in the differential diagnosis of sexual impotence.", Journal of Sex & Marital Therapy. 1975, 1(4), 277-289; and "Evaluation of nocturnal penile tumescence in the differention diagnosis of sexual impotence"; Archive of General Psychiatry, 1979, 36, 431-437) and Karacan (see "Clinical value of nocturnal erection in the prognosis and diagnosis of impotence," Medical Aspects of Human Sexuality, 1970, 4, 27-34; see also U.S. Pat. No. 4,103,678), has become the most widely used technique to establish a differential diagnosis between an organic and a psychogenic erectile dysfunction. Such a diffferential diagnosis appears to be essential for the implementation of therapeutic interventions, which can range from vascular surgery to psychoanalysis.
The standard method for measuring NPT makes use of a mercury strain gauge comprising a loop-shaped silastic tubing filled up with mercury. The tubing is positionned around the patient's penis and is connected to an electrical circuit for measuring its electrical resistance. Any change in the penile circumference causes stretching of the mercury column within the silastic tubing. Such a stretching in turn triggers a change in the mercury resistance, which can be translated into penile circumference increases.
If measurement of NPT remains an invaluable tool for diagnostic purposes, it has proved to be inefficient to measure penile rigidity, which can be defined as the state of penile firmness which is sufficient to allow vaginal penetration. Such a state of firmness can be translated into a measure of penile pressure. Since the silastic tubing used as NPT strain gauge, has an inherent elastic property, it is drastically restricted in use to the measurement of penile circumference and cannot accurately measure changes in penile pressure.
Several authors have emphasized the importance of assessing penile rigidity, in addition to NPT, in order to establish a more define differential diagnosis between organic and psychogenic erectile dysfunction. Clinical reports indicate that 17% of the patients who show normal penile tumescence on NPT recordings, actually have insufficient penile rigidity to allow vaginal penetration.
Various techniques have been developped to assess penile rigidity.
Some authors have used inferential techniques based on NPT recordings, such that 80% of maximal penile tumescence or 15 mm increase in penile circumference, correspond to sufficient penile rigidity to allow vaginal penetration. Dhabuwala et al (see "Penile calibration for nocturnal penile tumescence studies", Urology, 1983, 22, 614-616) however, have showed that the percentage of maximal tumescence required for sufficient penile rigidity varies between 53% and 92% across individuals. Such inter-subject variability makes the use of inferential techniques questionable.
Other investigators have used a waking method to directly assess penile rigidity. Some authors have asked the subjects to directly estimate the extent of penile rigidity during nocturnal erections, while others have estimated rigidity in conjunction with subject estimates. Karacan (see above) went a step further, and attempted to objectively measure penile rigidity using the buckling force technique. Once erection was observed from NPT, two constraint gauges were placed on the penile shaft and a constant weight, which does not usually triggers noticeable flexion of the penis, was applied on the glans penis. If the buckling force involves flexion of the penis, the author concludes that penile rigidity is insufficient to allow vaginal penetration. Although this technique presents advantages over subjective evaluations, it does not allow precise measurement of penile rigidity and it remains vulnerable to individual variability.
Other investigators have devised a technique consisting of surrounding the penile shaft with a continuous ring of stamps (see U.S. Pat. No. 4,474,187). Upon awakening in the next morning, the patient inspects whether the stamp ring has been broken. If so, the authors conclude that erection was sufficient to allow vaginal penetration. Although this method is an improvement over subjective evaluations, it remains vulnerable to extraneous variables such as the patient movements during the night, or the degree of humidity of the penis, which can both brake the stamp ring. Moreover, this method does not indicate the duration of the erection.
Other more objective measurements of penile rigidity have been investigated. Ek et al. (see "Nocturnal penile rigidity measured by the snap-gauge band", The Journal of Urology, 1983, 129, 964-966) have devised a snap-gauge band with three plastic films that have releasing forces of 10, 15, and 20 onces, respectively. Upon erection, the tearing of a given plastic film indicates the amount of force expended, which reflects penile rigidity. The procedure, however, does not allow continuous measurement of penile rigidity, and does not indicate the frequency and the duration of nocturnal erections.
Meehan and Golstein (see "High pressure within corpus cavernosum in man during erection. Its probable mechanism", Urology, 1983, 21, 385-387) have suggested to use a lucite cuff device consisting of two semi-circular metal plates attachable to each other over an erected penis by means bolts. The plates hold a small test bladder against a lateral aspect of the penis. The bladder is connected to a pressure transducer which is itself connected to an amplifier with recorder. In use, the bladder is filled up progressively with a seryngue to compress the penis while the pressure is being measured. As the bladder starts to compress the penis, a plateau in the pressure rise can be noted, which can be taken as a measure of the intracorporal pressure. This particular method is interesting but is very uncomfortable for the patient. In addition, this method is an "active" method which requires the presence of a doctor or a nurse to carry out the testing.
The U.S. firm DACOMED of Minneapolis has also devised a "rigiscan" consisting of a loop that self-adjusts over the penis. Upon discrete intervals, the loop constricts over the penis and a mechanic force is applied, and translated into a measure of penile rigidity.
Virag et al. (see "A new device for measuring penile rigidity," Urology, 1985, 25, 80-81) have developed a device consisting of a sensor supported by a metallic arch. The sensor covers one third of the penile circumference and is attached to an elastic strip which surrounds the remaining two third of the penis. The device is connected to an electronic dynamometer which translates morphologic changes of the penis into a measure of penile rigidity.
The above methods and devices represent definite advancements in the assessment of penile rigidity. The Dacomed's device, however, involves relatively numerous and expensive computer equipment, and its validation, which uses the buckling force devised by Karacan, is to be improved. The Meehan and Golstein technique as well as the Virag et al. technique both relate penile rigidity to ICP measures, which provides adequate validation for their measuring devices. The Meehan and Goldstein device, however, is very uncomfortable for the patients and can of course not be used over an entire night of testing, while the patient is sleeping. On the other hand, The Virag et al device makes use of an elastic penile cuff, which obviously curtails accurate measurements.